Amesite

Amesite
General
CategoryPhyllosilicates
Kaolinite-serpentine group
Formula
(repeating unit)		Mg2Al2SiO5(OH)4
IMA symbolAme[1]
Strunz classification9.ED.15
Crystal systemTriclinic
Crystal classPedial (1)
(same H-M symbol)
Space groupC1
Unit cella = 5.307(1), b = 9.195(2)
c = 14.068(3) [Å]
α = 90.09(2)°
β = 90.25(2)°, γ = 89.96(2)°; Z = 4
Identification
ColorWhite, colorless, pink to lilac, pale green
Crystal habitCrystals form as platy to tapering elongated pseudohexagonal prisms
TwinningCommon as six-fold sector twins on {001} and polysynthetic twins parallel to {010}
CleavagePerfect on {001}
TenacityBrittle
Mohs scale hardness2.5–3
LusterPearly
StreakWhite with pale green tint
DiaphaneityTransparent to translucent
Specific gravity2.77
Optical propertiesBiaxial (+)
Refractive indexnα = 1.597 nβ = 1.599 nγ = 1.615
Birefringenceδ = 0.018
Other characteristicsKaolinite-serpentine group
References[2][3][4]

Amesite is a mineral with general formula of Mg2Al2SiO5(OH)4.[3]

Amesite crystallizes in the triclinic crystal system.[5] It contains three axes of unequal length, not at right angles.

It was first described in 1876 for an occurrence in the Chester Emery Mines, Chester, Hampden County, Massachusetts. It was named for mine owner James Ames.[4][3] It occurs in an environment of low-grade metamorphism affecting rocks with high aluminium and magnesium content. It occurs associated with vesuvianite, chlorite, magnetite, rutile, diaspore, grossular, calcite, diopside and clinozoisite in various locations.[2]

Amesite is an uncommon silicate mineral which has been reported from a variety of locations worldwide.[3] Amesite has the first reported natural occurrence of the 6R polytype for a trioctahedral 1:1 layer silicate.[6]

References

  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ a b Handbook of Mineralogy
  3. ^ a b c d Mindat.org
  4. ^ a b Webmineral data
  5. ^ Roberts, W.L. (1974) Encyclopedia of Minerals, p. 18. Van Nostrand Reinhold Company, New York, New York.
  6. ^ Hall, Stephen H; Bailey, S.W. (5 January 1976). "Amesite From Antartica" (PDF). American Mineralogist. 61: 497–499. Retrieved 28 October 2022.


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